Re: [PATCH 2/2] KVM: PPC: Replay pending interrupts before entering the guest

[Narayana Murty N <nnmlinux@linux.ibm.com>]

Hi Shrikanth,

On 28/09/26 4:34 PM, Shrikanth Hegde wrote:
> After applying preempt disable patch, i.e PATCH 1/2, Christian reported
> a subsequent warning stopping his board to boot properly.
> 
> WARNING: at .kvmppc_fix_ee_before_entry+0x10/0x28, CPU#0: qemu-system-ppc/4667
> CPU: 0 UID: 1000 PID: 4667 Comm: qemu-system-ppc Tainted: G        W           7.3.0-rc4-2-powerpc64-smp #1 PREEMPT
> Tainted: [W]=WARN
> Hardware name: varisys,CYRUS5040 e5500 0x80240012 CoreNet Generic
> NIP [c00000000005dc3c] .kvmppc_fix_ee_before_entry+0x10/0x28
> LR [c00000000005f298] .kvmppc_handle_exit+0x5b4/0x5e8
> Call Trace:
> [c000000086587780] [c00000000005ee10] .kvmppc_handle_exit+0x12c/0x5e8 (unreliable)
> [c000000086587830] [c000000000062068] .kvmppc_resume_host+0xb8/0x10c
> 
> It triggers below warning...
> 
> static inline void kvmppc_fix_ee_before_entry(void)
> {
>          trace_hardirqs_on();
> 
>          /*
>           * To avoid races, the caller must have gone directly from having
>           * interrupts fully-enabled to hard-disabled.
>           */
>          WARN_ON(local_paca->irq_happened != PACA_IRQ_HARD_DIS);
> 
> This happens since kvmppc_prepare_to_enter does first local_irq_disable
> followed by hard_irq_disable. This leaves a small window where interrupt
> may occur and it could set the irq pending bit in PACA. When that
> happens replay that interrupt before entering the guest.
> 
> Fixes: 12013e3d4695 ("KVM: powerpc: Use generic xfer to guest work function")
> Reported-by: Christian Zigotzky <chzigotzky@xenosoft.de>
> Closes: https://lore.kernel.org/all/b8f82519-9ae5-c247-e020-e79c627e57df@xenosoft.de/
> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
> ---
>   arch/powerpc/kvm/powerpc.c | 13 +++++++++++++
>   1 file changed, 13 insertions(+)
> 
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index 9194cf492d1c..847ff07c364b 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -147,6 +147,19 @@ int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
>   			continue;
>   		}
>   
> +#ifdef CONFIG_PPC64
> +		/*
> +		 * Interrupt arrived between the soft and hard
> +		 * disable. Replay it and retry guest entry.
> +		 */
> +		if (unlikely(local_paca->irq_happened != PACA_IRQ_HARD_DIS)) {
> +			local_irq_enable();
> +			local_irq_disable();
> +			hard_irq_disable();
> +			continue;
> +		}
> +#endif
> +
>   		guest_enter_irqoff();
>   		return 1;
>   	}

It look good to me.

Thanks,
Narayana